Molecular Geometry VSEPR - Valence Shell Electron Pair Repulsion Theory. In small molecules, electrons and bonds are arranged as far apart as possible.

Molecular Geometry This allows for atoms to have 3-D shapes different from their shapes in 2-D (paper).

Molecular Geometry Linear – the bonds form a straight line. Example CO 2 Bond Angle 180⁰ [

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Molecular Geometry Trigonal Planar– The central atom has only 3 bonds. Example: CH 2 O (Formaldehyde) Bond angle 120⁰ [ r_Resources/Chapter_10/FG10_00-66c.JPG]

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Molecular Geometry Tetrahedral –The central atom has only 4 bonds Example: CH 4 (methane) Bond Angle 109.5⁰ [ s/476/488316/Instructor_Resources/Chapt er_10/FG10_00-69d.JPG]

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Molecular Geometry Trigonal Pyramidal – Central atom has 3 bonds and one lone pair of electrons that “pushes” the bonds away. Example: NH 3 (ammonia)

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Molecular Geometry Bent – Here there are two bonds and two pairs of electrons on the central atom. Example: H 2 O (water) [

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Polarity When 2 atoms in a bond have different electronegativity values, electrons can be “pulled” more toward one side of the bond. A bond where this occurs is called a dipole.

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Polarity Showing Polarity “Minus” sign above the high electronegative atom. “Plus” sign over the other atom. Draw arrow from plus to minus. [

Compound Polarity Draw a correct 2-D compound with arrows along each bond. Example: CH 4 CH H H H

Compound Polarity Then, check to see if any of the arrows cancel out. To do this think “tug of war” CH H H H

Compound Polarity If all arrows cancel out, the molecule is non-polar or covalent. If the arrows do not cancel out, the molecule is polar or polar-covalent.

Compound Polarity Remember: 3D shape determines 2D drawing. Example: H 2 O HHO H H O